Multilayer coated substrate

Abstract

A process for electrostatically applying a multilayered coating on a substrate in one operation or step is disclosed, wherein a mixture of powders of at least two different coating materials is used as the coating composition, each powder, in the case of non-conducting powders, differing from the others in dielectric constant by a factor of at least 0.1, and the powders being of substantially different specific gravities, with the components having the lowest dielectric constant value having the lowest specific gravity value. At least one of the powders will be a powder of a film-forming non-conductive organic or inorganic polymer. Upon electrostatically applying a coating of this powdered composition to a conductive substrate which has a neutral charge or a charge opposite from that of the coating composition powder particles, the powders stratify into distinct layers of different compositions. The powders adhere to the substrate because of contact or static electrification for a reasonable length of time and until at least one of the powders can be cured or fused to form the final coating. Thus, for instance, in only one pass with an electrostatic spray gun, a protective coating of superimposed layers of zinc, epoxy, and polyethylene can be applied to a conductive substrate.

We claim: 
     
       1. An article of manufacture consisting essentially of a conductive substrate and, adjacent and overlying said conductive substrate, a coating comprising a plurality of superimposed, distinct layers, the layer next to the conductive substrate consisting essentially of a layer of conductive metal selected from the group consisting of iron, stainless steel, zinc, copper, nickel, tin, chromium, brass, titanium, zirconium, lead and alloys of these metals,   at least one of said layers consisting essentially of at least one first film-forming non-conductive organic or inorganic polymer,   the specific gravity of said conductive metal being at least three times that of said first polymer,   said coating being applied to said conductive substrate in one step by electrostatically applying an admixture of powders, said admixture including powders having average particle sizes less than 50 microns of said conductive metal and powders having average particle sizes of about 10 to 300 microns of said first polymer, whereby said powders stratify into distinct, overlying layers, and thereafter curing or fusing at least one of said powders,   whereby the superimposed layers of the coating exhibit improved adhesion as compared to similar articles wherein the coating layers are separately applied and cured or fused.   
     
     
       2. Article of claim 1, wherein the conductive metal layer is about 4 to about 30% by weight of the weight of said coating. 
     
     
       3. Article of claim 1, wherein said first polymer is an organic polymer. 
     
     
       4. Article according to claim 1, wherein said first film-forming non-conductive organic or inorganic polymer is a thermosetting or thermoplastic organic polymer. 
     
     
       5. Article according to claim 4, wherein said polymer is a thermosetting organic polymer. 
     
     
       6. Article of claim 1, wherein said first polymer is an epoxy polymer, said metal is zinc. 
     
     
       7. Article according to claim 6, wherein the zinc is present in an amount less than 7 1/2% by weight of said coating. 
     
     
       8. Article of claim 1, wherein said coating comprises at least three layers, at least one of the layers consisting essentially of at least one second film forming non-conductive organic or inorganic polymer, wherein the second polymer has a dielectric constant which is at least 0.1 lower than the dielectric constant of the first polymer, and the specific gravity of the second polymer is at least 0.1 lower than the specific gravity of the first polymer. 
     
     
       9. Article according to claim 8, wherein one organic polymer is a thermosetting organic polymer, and the other organic polymer is a thermoplastic organic polymer, the layer of said metal being about 5 to about 12% by weight of said coating, the layer of thermosetting organic polymer being about 55 to about 75% by weight of the weight of said coating, the weight of said thermoplastic polymer layer being about 20 to about 40% by weight of said coating wherein the thermosetting organic polymer has a dielectric constant which is at least 0.1 higher than the dielectric constant of the thermoplastic organic polymer, and the specific gravity of the thermosetting organic polymer is at least 0.1 higher than the specific gravity of the thermoplastic organic polymer. 
     
     
       10. Article according to claim 9, wherein said thermosetting polymer is an epoxy polymer, and said thermoplastic polymer is polyethylene.